The function of a holding brake is to hold an elevator stationary at a floor and also to stop the elevator car or prevent its motion during a power failure. Therefore, the braking action of the holding brake is based on a mechanical pressure element, such as a spring, which keeps the brake engaged when there are no external forces acting on it. As the holding brake is activated each time when the car arrives at a floor and releases each time the car leaves a floor, its operation must be as fast, accurate and noiseless as possible so that it will not be noticed by elevator users. For this reason, the air gap between the brake shoe of the holding brake and the traction sheave or a possible separate brake wheel must be as narrow as possible to allow the braking to occur as quickly as possible and to keep the impact energy of the brake shoe as low as possible and the locking of the brake as noiseless as possible. On the other hand, it is to be noted that there must be a definite air gap between the brake shoe and the braking surface and that the brake shoe must not chafe the braking surface as this would result in undesirable noise during elevator travel.
In holding brakes used at present in traction sheave elevators, i.e. in normal slide brakes, bearing tolerances in the brake lever systems and structural deflections impair the accuracy of the braking action, which is why it is necessary to use relatively large air gaps in holding brakes. Therefore, the required movements in the brake shoe and in the parts actuating it are large, implementing the movements requires relatively large and expensive components, and the braking action produces a relatively noisy impact due to the large air gap. Especially the electromagnet used to release the brake is relatively large and expensive due to the long brake shoe travel upon release of the brake.